This invention relates generally to a system and method for executing an aircraft circle-to-land maneuver, and more specifically to a system and method for executing a circle-to-land maneuver using the airborne area navigator.
A circle-to-land (xe2x80x9cCTLxe2x80x9d) maneuver is one of the most challenging maneuvers required of flight crews. The CTL maneuver is used when an aircraft approaches an airport on an approach path that does not align with the favored runway. For large commercial airliners, and especially for such aircraft at large commercial airports, the CTL maneuver is not usually an issue because air traffic controllers at those airports can usually direct commercial aircraft to a straight in landing. With smaller aircrafts at smaller airports, however, a CTL maneuver becomes a more usual occurrence. Even the large commercial airliners, on occasion, have to perform a CTL maneuver.
A straight in landing may not be available and a CTL maneuver may be required, for example, because of inclement weather or traffic around the airport. At some airports a CTL maneuver is necessitated by limited air traffic control facilities. In yet other instances an airport may have a straight in instrument approach procedure, but local weather conditions or other constraints favor another runway that does not have such an approach. Under these conditions the initial approach to the airport may be straight in, but the flight crew must then resort to a CTL maneuver. In other instances navigational aids (xe2x80x9cNAVAIDSxe2x80x9d) direct the aircraft to the center of the airport rather than to the end of the runway. The flight crew must then perform the CTL maneuver to align with the appropriate runway. The pilot must use visual cues to maneuver the aircraft to downwind, base and final. This maneuvering is done manually or by using limited automation available today from a flight guidance computer (xe2x80x9cFGCxe2x80x9d).
CTL maneuvers are performed at low altitude using visual cues such as runway lights. The CTL maneuver is very difficult in poor weather, at night time, or in other conditions of low visibility. During the CTL maneuver, the pilot is responsible for keeping the aircraft in protected air space. Landing an airplane, always a difficult task, becomes more difficult during a CTL maneuver because of the high work load experienced by the flight crew during the maneuver.
In view of the difficulty and hazard associated with a CTL maneuver, a need clearly exists for an automated procedure for controlling an aircraft in a CTL maneuver that would reduce the workload for the flight crew and increase safety.
In accordance with one embodiment of the invention, a flight control system is provided to control a circle-to-land (xe2x80x9cCTLxe2x80x9d) maneuver of an aircraft. The flight control system makes use an airborne area navigator (herein referred to as xe2x80x9carea navigatorxe2x80x9d) installed on the aircraft. The area navigator receives inputs on aircraft position and velocity, airport navigation data, and pilot supplied data. In response to those inputs, the area navigator provides steering and other control commands to an onboard flight director. The area navigator also provides such commands to the aircraft pilot. The pilot has the option of executing the CTL maneuver manually using the provided information or allowing the aircraft autopilot to execute the maneuver under the control of the flight director.